1. Field of Invention
The present invention relates to an electrostatic discharge protection apparatus. More particularly, the present invention relates to an electrostatic discharge protection apparatus for a multi-hole structure.
2. Description of Related Art
Electronic devices, such as monitors, notebook computers and mobile telephones, are easily damaged by electrostatic discharge (ESD) that affects normal operations of these electronic devices. The transient voltage induced by electrostatic discharge is very large, and as the scale of integrated circuit elements is reduced, the threshold electrostatic voltage that may cause electrostatic discharge also becomes smaller. In practical use, some high-speed electronic devices may be damaged when the magnitude of the electrostatic is only 30 V.
The reason of electrostatic discharging is because an electric field formed by charged objects ionizes surrounding gases to induce discharge. Both conductors and nonconductors can induce and accumulate electric charges. Generally, a material with low resistance easily dissipates electric charges, but a material with high resistance dissipates electric charges with difficulty. For this reason, nonconductors very easily accumulate electrostatic charges. Artificial polymers, like plastics, are able to gather and keep electrostatic charges for a long time due to their high resistance.
Electrostatic discharges include direct electrostatic discharges and indirect electrostatic discharges. The direct electrostatic discharges are further divided into contact discharge and air discharge according to their different discharge methods. The indirect electrostatic discharges are also further divided into horizontal coupling place (HCP) discharge and vertical coupling place (VCP) discharge.
Many kinds of anti-electrostatic discharging software and hardware are provided to avoid the electrostatic discharges damage electronic devices. For nonconductors, a method for avoiding accumulating a large quantity of electric charge is to apply a coating of anti-electrostatic material, such as carbon powder, anti-static agents, or metal films on their surfaces. The anti-electrostatic materials on surfaces of nonconductors form a conductive layer to dissipate accumulated charges to other places. Another method is to add carbon powder, anti-static agents, metal powder, or metal fibers into nonconductors during production thereof to convert nonconductors into anti-electrostatic material or conductors.
Grounding is the most effective and efficient way to avoid electrostatic discharge. Electric charges accumulated on an object discharging all energies in one electrostatic discharge are the main reason for the fatal damage caused by electrostatic discharge. Accordingly, connecting all objects together, then grounding, and keeping low resistance between them can dissipate electric charges accumulated thereon to the ground, and thus avoids the damage caused by electrostatic discharge.
Manufacturers usually apply ESD tests to the electronic devices to ensure capability of resisting electrostatic discharge and maintenance of a steady condition. The environment of the ESD test is a temperature of: 15° C.−35° C.; relative humidity: 30%–60%; and an atmospheric pressure of: 68 Kpa (680 mbar)–106 Kpa (1060 mbar). The ESD test simulates electrostatic discharge to test whether electronic devices effectively avoid electrostatic discharge under different discharging conditions.
FIG. 1A illustrates a schematic view of a conventional notebook computer. The notebook computer 100 includes a covering case 102 and a body 104. The covering case 102 is usually composed of artificial polymers, like plastics, to reduce the weight and the manufacturing expenses thereof. The body 104 includes a speaker 114 that is an electronic device. The speaker 114 is located in a speaker output port 112, which facilitates sound emission of speaker 114.
FIG. 1B illustrates a schematic back view of the covering case in FIG. 1A. The surface of the covering case 102 easily accumulates electric charges because its material is a nonconductor, like plastic. A prior method to dissipate electric charges accumulated on the covering case 102 is the addition of a conductive layer 122 on an inside surface thereof, for example, spreading conductive lacquer on the inside surface. The electric charges accumulated on the surface of the covering case 102 are thus dissipated to the ground, and damage caused by electrostatic discharge is avoided.
However, the speaker output port 112 on the covering case 102 is a multi-hole structure. The multi-hole structure includes many and dense holes, which facilitates sound generation of the speaker 114. The conductive lacquer squeezes out through the multi-hole structure onto the outside surface of the covering case 102 during spreading. Hence, conductive layer 122 is usually not added to the inside surface of the covering case 102 where the speaker output port 112 located, for fear of the conductive layer 122, such as a conductive lacquer, soiling the appearance of the notebook computer 100. In the ESD test of the notebook computer 100, the speaker output port 112 generally fails the ESD test because of the inside surface thereof lacks the conductive layer 122.